1. Field of the Invention
The present invention relates to a wireless communications device having an access point function of a wireless network, an electronic apparatus including the wireless communications device, and methods for determining and updating an access point.
2. Description of the Related Art
Wireless local area network (LAN) technologies have been globally popularized in offices and homes. The wireless LAN technologies are standardized by the 802.11 task group of the Institute of Electrical and Electronic Engineers (IEEE), which sets the standards for wireless LAN, known as 802.11a, 802.11g, and 802.11n.
802.11a specifies communications using the 5-GHz frequency range. 802.11g specifies communications using the 2.4-GHz frequency range. 802.11n relates to a wireless communications technique such as multiple input multiple output (MIMO) by which the frequency range for transmitting and receiving data is expanded by combining a plurality of antennas on a transmission side and a receiving side.
As specified by 802.11a/11g/11n, the communications mode is classified into two modes of an infrastructure mode and an ad-hoc mode.
In the infrastructure mode, wireless communications devices serving as wireless LAN terminals are provided around an access point and data is transmitted between one of the wireless communications devices and the other wireless communications device through the access point. The infrastructure mode is a general communications mode mostly used in offices and homes.
On the other hand, in the ad-hoc mode, data is directly transmitted between the wireless communications devices and no access point is provided. That is, the ad-hoc mode requires no access point. When communications in the ad-hoc mode (hereinafter referred to as ad-hoc communications) is made among a plurality of wireless communications devices, each wireless communications device needs to grasp the states of the whole wireless communications devices included in a network. Therefore, there are many cases in which functions such as a transmission rate control function and authentication function are limitedly used. In addition, setting methods for communications are also cumbersome. As a result, the specifications of 802.11a/11g/11n have been only used as an auxiliary communications method.
Recently, the wireless LAN communications functions have been included in devices serving as compact terminals such as cellular phones, digital cameras, printers, and portable audio equipment in addition to the devices serving as the information communication terminals such as personal computers (PCs). Of course, such devices can perform communications through an access point. However, when data is transmitted only between the devices, e.g., the communications between the digital camera and the printer, it is easier and more convenient to directly perform communications therebetween in an ad-hoc-like manner without the access point than to perform communications through the access point.
For example, the Wi-Fi Alliance, which is a trade association devoted to promoting use of wireless LAN products, has been examining specifications for wireless communications setting methods and connection methods for making direct communications between the communications terminals such that the ad-hoc mode is more easily used.
For example, Wi-Fi Peer-to-Peer (P2P) Technical Specification Version 1.1 describes a basic concept of Wi-Fi Direct. According to the basic concept, in a network including a plurality of wireless communications devices each having a simplified access point function, one of the wireless communications devices practically operates as the simplified access point. The simplified access point that behaves like the typical access point enables connection procedures of a maximum transmission rate and an encryption method to be performed in the same manner as the infrastructure mode even though in the ad-hoc mode.
More specifically, in Wi-Fi P2P Technical Specification Version 1.00, each wireless communications device attending a wireless LAN is defined as a Peer to Peer (P2P) device and the network is defined as a P2P group. In the P2P group, the P2P device that practically uses the simplified access point function is defined as a P2P group owner and the other P2P devices other than the P2P group owner are defined as P2P clients. A procedure to determine the P2P group owner among the P2P group devices is defined as a group owner negotiation.
FIG. 12 is a sequence diagram illustrating a procedure in which wireless communications devices 1000 and 2000 that are the P2P devices perform the group owner negotiation after both devices search for connection partners. The wireless communications devices 1000 and 2000 have the same structure. The following description is made on a case where the wireless communications device 2000 starts the searching operation.
As illustrated in FIG. 12, first, the wireless communications device 2000 transmits a probe request frame (sequence S101). Upon receiving the probe request frame, the wireless communications device 1000 sends a probe response frame back (sequence S102).
Upon receiving the probe response frame, the wireless communications device 2000 recognizes the presence of another wireless communications device at a place at which communications can be made with the wireless communications device 2000, transmits a group owner (GO) negotiation request frame, and starts the group owner negotiation (sequence S103). The GO negotiation request frame includes a P2P information element (P2P IE) and a Wi-Fi protected setup information element (WPS IE). The P2P IE includes various types of information such as a group owner intent value that is a parameter indicating a level of intention to serve as the P2P group owner and a “channel” that indicates channels supported by the device. The group owner intent value can be set to an integer between 0 to 15, inclusive.
Upon receiving the GO negotiation request frame, the wireless communications device 1000 sends the GO negotiation response frame back (sequence S104). The GO negotiation response frame includes the P2P IE including the group owner intent value and the “channel” in the same manner as the GO negotiation request frame.
Upon receiving the GO negotiation response frame, the wireless communications device 2000 determines the P2P group owner by the procedure of the flowchart illustrated in FIG. 13, and notifies the wireless communications device 1000 of the determination result with a GO negotiation confirmation frame (sequence S105). Upon receiving the GO negotiation request frame, the wireless communications device 1000 also determines the P2P group owner by the procedure of the flowchart illustrated in FIG. 13. That is, the wireless communications devices 1000 and 2000 individually determine the P2P group owner by the same procedure. The operation of the wireless communications device 2000 is described below.
As illustrated in FIG. 13, the wireless communications device 2000 determines whether a group owner intent value x1 of the wireless communications device 1000 is equal to the group owner intent value x2 of the own device (step ST101). If it is determined that they are not equal (NO at step ST101), the wireless communications device 2000 determines a magnitude relationship between x1 and x2 (step ST102) and determines the wireless communications device having a larger group owner intent value as the P2P group owner (steps ST102 to ST104). That is, if the group owner intent value x2 of the wireless communications device 2000 is larger (YES at step ST102), the wireless communications device 2000 determines the wireless communications device 2000 as the P2P group owner (step ST103). If the group owner intent value x1 of the wireless communications device 1000 is larger (NO at step ST102), the wireless communications device 2000 determines the wireless communications device 1000 as the P2P group owner (step ST104).
If the group owner intent values of the wireless communications devices 1000 and 2000 are equal to each other (YES at step ST101), the wireless communications device 2000 determines whether they are less than 15 (step ST105). If they are less than 15 (YES at step ST105), the wireless communications device 2000 determines the wireless communications device having a tie break bit value of 1 as the P2P group owner (step ST106).
The tie break bit value is randomly set to 1 or 0 by the wireless communications device that issues the GO negotiation request and transmitted by being included in the GO negotiation request frame. The tie break bit value included in the GO negotiation request frame is toggled and sent back by being included in the GO negotiation response frame.
Specifically, when the group owner intent values of the wireless communications devices 1000 and 2000 are less than 15 and are equal to each other, if the wireless communications device 2000 sets the tie break bit value to 1 and transmits the GO negotiation request frame, the wireless communications device 2000 is determined as the P2P group owner while if the wireless communications device 2000 sets the tie break bit value to 0 and transmits the GO negotiation request frame, the wireless communications device 1000 is determined as the P2P group owner.
If the group owner intent values of the wireless communications devices 1000 and 2000 are 15 (NO at step ST105), the wireless communications device 2000 determines that the determination procedure of the P2P group owner has failed (step ST107).
In this way, the connection method described in the Wi-Fi P2P technical specification Version 1.00 can determine the wireless communications device serving as the simplified access point and the P2P communications can be made between the devices without using the access point terminal.
The P2P group owner performs the functions of the access point. For example, the P2P group owner allocates addresses to wireless communications devices (P2P clients) to be connected, performs synchronization with a beacon signal, and serves as a mediator of data communications between wireless communications devices through the simplified access point. That is, the P2P group owner processes loads heavier than those processed by the P2P clients.
In the wireless communications, power is consumed by radio emission. Thus, the more a signal transmission amount increases the more power consumption increases. Therefore, the P2P device having enough power for maintaining the network should be determined as the P2P group owner. For example, the P2P device to be determined as the P2P group owner preferably receives power from an alternating-current (AC) power supply (outlet).
The access point terminal device performing communications in the infrastructure mode is installed fixedly, and generally receives the power from the AC power supply. Thus, the power for maintaining the wireless network does not need to be taken into consideration for such the access point terminal device. On the other hand, in the ad-hoc communications, all of the devices do not always stably receive the power because the battery-driven devices having compact sizes such as the cellular phones and the digital cameras form the wireless network as described above.
In the group owner negotiation described in the Wi-Fi P2P technical specification Version 1.00, however, the group owner intent value and the tie break bit value of each P2P device are used as the criteria for determining the P2P group owner, but the power supply status is not taken into consideration. As a result, after the P2P group is formed, the network may be disconnected because the insufficient remaining battery charge of the P2P group owner causes the network not to be maintained.
Therefore, there is a need for technology capable of reducing possibility of disconnecting a wireless network due to a power shortage to drive a wireless communications device serving as an access point in the wireless network including a plurality of wireless communications devices each having an access point function of the wireless network.